NH-2176 - one more concurrency issue, but not sure that will fix it.

Author: fredericDelaporte

src/NHibernate/Transaction/AdoNetWithDistributedTransactionFactory.cs

@@ -170,6 +170,9 @@ void IEnlistmentNotification.InDoubt(Enlistment enlistment)
 
 			private void ProcessSecondPhase(Enlistment enlistment, bool? success)
 			{
+				// In case of rollback, the prepare phase may have not be run, and we then need to lock as soon as possible.
+				// There is no guarantee the second phase will be run before the completed event, doing that at both places.
+				SafeLockSession();
 				using (new SessionIdLoggingContext(_sessionImplementor.SessionId))
 				{
 					_logger.Debug(
@@ -195,6 +198,9 @@ private void ProcessSecondPhase(Enlistment enlistment, bool? success)
 
 			public void TransactionCompleted(object sender, TransactionEventArgs e)
 			{
+				// In case of rollback, the prepare phase may have not be run, and we then need to lock as soon as possible.
+				// There is no guarantee the second phase will be run before the completed event, doing that at both places.
+				SafeLockSession();
 				e.Transaction.TransactionCompleted -= TransactionCompleted;
 				// This event may execute before second phase, so we cannot try to get the success from second phase.
 				// Using this event is required by example in case the prepare phase failed and called force rollback:
@@ -247,6 +253,23 @@ private void RunAfterTransactionActions(bool wasSuccessful)
 				}
 			}
 
+			/// <summary>
+			///  Lock the session, but do not assume the context is not already disposed or concurrently disposing.
+			/// </summary>
+			private void SafeLockSession()
+			{
+				if (_isDisposed)
+					return;
+				try
+				{
+					_waitEvent.Reset();
+				}
+				catch
+				{
+					// Ignore, concurrently disposing, meaning it does not need to block anymore.
+				}
+			}
+
 			private volatile bool _isDisposed;
 
 			public void Dispose()